1. Field of Invention
The present invention relates to a task scheduling method, and more particularly, to a dynamic voltage scaling scheduling method for sporadic and hard real-time tasks with resource sharing.
2. Related Art
An embedded system is a device for controlling, monitoring, or assisting the operation of an apparatus, a machine, or even a factory, which is a combination tightly integrated with computer software and hardware. In newly-emerged embedded system products, the most common ones include mobile phone, PDA, GPS, Set-Top-Box, embedded server, and thin client.
The embedded system has a lot of differences with the desktop computer system, and the microprocessor of most embedded systems is developed in manner of SoC. As for the flow of developing software, the software of the embedded system always exists in form of a firmware, therefore, the development in terms of software is also different from the development of desktop computer programs, and it is very common for the development of embedded system to develop software and hardware at the same time.
Most of the current embedded systems are developing towards the trend of being mobile, networked, and automatic. Since the executed software modules always have the real-time requirement and are limited by the electric power, how to achieve the real-time task scheduling that meets the highest energy-saving requirement has always been an important key technique in the real-time operating system used in the current embedded system.
In the currently existed techniques, multitasking scheduling is mostly achieved with fixed voltage and time division, or the energy-saving objective is achieved by way of static voltage scaling through using multilevel voltage scaling. The tasks are designated with different priority levels, the processing time is allocated according to the priority levels, and thus the tasks with different priority levels can obtain different processor time and different executing order. On the other hand, the energy-saving objective is achieved by setting different executing voltages according to different power supply states and task requirements. The current mechanism has an easy implementation manner, and does have the energy-saving effect, however, it can only be applied in a common computer architecture with several and discrete voltage levels, but cannot guarantee to meet the hard real-time requirement, thus it has a very limited performance in terms of energy-saving. In addition, when there are sporadic and resource-sharing tasks, it is hard to meet the hard real-time requirement.
Moreover, when considering the scheduling of a task set, the dependence between different tasks must be taken into consideration, for example, the accessing of the software resources for different tasks, so as to avoid excessive context switch, which consumes excessive electrical power.